In the 17th century, German scientist Otto von Guericke built and carried out experiments with a sulfur globe. He described the globe and its use in Experimenta Nova Magdeburgica de Vacuo Spatio (the same work in which von Guericke discusses his more famous device, the vacuum pump), published in 1672. Several of von Guericke’s experiments with the sulfur globe involved electricity, although he did not discuss them in electrical terms.
Like William Gilbert’s terrella, von Guericke considered his sulfur globe a model of the Earth. Instead of being magnetic, however, von Guericke’s globe was electric; at least it was after he rubbed its surface with his hand or a pad. Through rubbing, electrical charges built up on the globe’s surface. This kind of frictional charging of an object produces static electricity. The same process is responsible for the shock you get when you touch a door handle after shuffling your feet across the carpet, as well as the tendency of your hair to stand on end when you pull a knit cap off of your head in the winter. Once the sulfur globe acquired excess charge, von Guericke used it to observe a variety of phenomena that today we recognize as characteristic of static electricity. These phenomena included attraction, repulsion, leaping sparks visible in the darkness and crackling sounds.
To form his sulfur globe, von Guericke cast sulfur that had first been ground into a powder and then melted into a hollow ball of glass. Once the sulfur cooled and hardened, he broke the surrounding glass in order to expose the sulfur. He then perforated the sulfur globe so that it could be affixed to an iron rod. The rod served as an axle. It allowed the globe to be rapidly rotated with a handle while it was anchored on a wooden base. Fast rotation sped up the process of charging the surface of the globe. The base of von Guericke’s device contained drawers, in which he stored feathers, pieces of paper and other materials useful for demonstrations of the globe’s intriguing abilities. For experiments, the globe could be removed from its base.
Von Guericke included an illustration of his sulfur globe, similar to this one, in his 1672 treatise. He first made the globe, however, in the 1660s. More than a decade later, he noticed that sometimes when he rotated the sulfur globe, it glowed. Although von Guericke did not understand it, the glowing he observed was electroluminescence, the conversion of electric energy into light. No one ever reported seeing electroluminescence before von Guericke. Yet von Guericke did not always give an account of everything he saw during his studies. He slyly wrote in Experimenta Nova Magdeburgica de Vacuo Spatio, after describing several experiments with his sulfur globe, "Now many other mysterious facts which are displayed by this globe I shall pass by without mention. Nature often presents in very commonplace things marvelous wonders which are not discerned except by those who through insight and innate curiosity consult the oracle of experimentation." With this conclusion and his explicit instructions on how to build the sulfur globe, von Guericke made it possible for countless others to observe the wonders of electrostatics first hand.
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